Flat Panel Liquid Displays, particularly of the type utilizing an X,Y matrix of individual pixels arranged in a row and column format are well-known and useful in a variety of applications. Liquid Crystal Displays of this matrix type are usually twisted nematic cells and incorporate polarizers located on each side of the Liquid Crystal Display Panel with a light source positioned behind the Panel. Due to the nature of the arrangement of molecules in a namatic Liquid Crystal Display, light from a particular off-axis direction is not equally effective as light from another off-axis direction. That is, because of the nature of liquid displays, the angle from which the display is viewed can often affect contrast ratio, especially if the light is uncollimated.
A recently filed application, entitled "Light Source from Liquid Crystal Display Panel Utilizing Internally Reflecting Light Pipes", Ser. No. 941,002, filed Dec. 12, 1986, U.S. Pat. No. 4,735,495, in the name of John L. Henkes the inventor of the instant application, and assigned to General Electric Company assignee of the instant invention, describes a source of relatively collimated light for a Liquid Crystal Display. The collimated light system in the above identified application involves the use of a light integrating sphere having tapered light pipe means coupled thereto for producing a relatively collimated light output for illuminating a Flat Panel Liquid Crystal Display. In the collimated light source described in the above identified application, the light is collimated within a permissilbe collimation deviation, .+-.r as for example, .+-.10 or 11 degrees from absolute collimation; with the degree of collimation, i.e., lthe maximum deviation from absolute collimation, depending on the design of the Flat Panel Liquid Crystal Display.
In a collimated light source of this type,i.e., using a tapered light pipe or light pipes, it has been found that in addition to the permitted collimation deviation there is also an offset or skew angle of the collimated light as a function of distance from the axis of the light pipe to the edge of the light pipe or pipes and collimated light with the permitted deviation from collimation of .+-.r is skewed or offset from an axis orthogonal to the surface of the light pipe thus offsetting the light from the axis. This offset of the collimated light is undesirable as it may, in turn, cause problems due to the unequal effects of the offset collimated light.
Applicant has found that offset of the collimated light beam towards the edge of the collimating light pipes may be corrected by means of a secondary collimator positioned between the end of the light pipe collimator and the Flat Panel Liquid Crytal Display with the secondary collimator taking the form of crossed cylindrical lenses which bend the light back to compensate for the offset or deviation angle.
It is therefore a principal objective of the invention to provide a collimated light source for a Flat Panel Liquid Crystal Display in which an offset or skew of the collimated light is corrected.
Another objective of the invention is to provide a collimated light source for a Liquid Crystal Display utilizing tapered light pipes and secondary collimators for compensating for offset of the collimated light from the tapered light pipes.
Yet another objective of the invnetion is to provide a collimated light source for a Flat Panel Liquid Crystal Display utilizing accommodation of light pipes, an integrating light source and a secondary collimation element for compensating for offset or skew in the angle of collimated light emitted from the light pipes.
Other objectives and advantages of the invention will become apparent as the description proceeds.